I. 



THE DURATION OF LIFE. 



WITH your permission, I will bring- before you to-day some 

 thoughts upon the subject of the duration of life. I can scarcely 

 do better than begin with the simple but significant words of 

 Johannes Miiller : ' Organic bodies are perishable ; while life main- 

 tains the appearance of immortality in the constant succession of 

 similar individuals, the individuals themselves pass away.' 



Omitting-, for the time being*, any discussion as to the precise 

 accuracy of this statement, it is at any rate obvious that the life of 

 an individual has its natural limit, at least among those animals 

 and plants which are met with in every-day life. But it is equally 

 obvious that the limits are very differently placed in the various 

 species of animals and plants. These differences are so manifest 

 that they have given rise to popular sayings. Thus Jacob Grimm 

 mentions an old German saying, ' A wren lives three years, a dog 

 three times as long as a wren, a horse three times as long as a dog, 

 and a man three times as long as a horse, that is eighty-one years. 

 A donkey attains three times the age of a man, a wild goose three 

 times that of a donkey, a crow three times that of a wild goose, a 

 deer three times that of a crow, and an oak three times the age of 

 a deer.' 



If this be true a deer would live 6000 years, and an oak nearly 

 20,000 years. The saying is certainly not founded upon exact obser- 

 vation, but it becomes true if looked upon as a general statement 

 that the duration of life is very different in different organisms. 



The question now arises as to the causes of these great differ- 

 ences. How is it that individuals are endowed with the power 

 of living long in such very various degrees ? 



One is at first tempted to seek the answer by an appeal to the 

 differences in morphological and chemical structure which separate 



